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Dresden 2020 – wissenschaftliches Programm

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HL: Fachverband Halbleiterphysik

HL 48: Organic semiconductors II (joint session HL/CPP)

HL 48.7: Vortrag

Mittwoch, 18. März 2020, 17:15–17:30, POT 112

Reverse Dark Current in Organic Photodetectors — •Jonas Kublitski1, Andreas Hofacker1, Christina Kaiser2, Donato Spoltore1, Hans Kleemann1, Axel Fischer1, Koen Vandewal3, and Karl Leo11IAPP - TU Dresden, Germany — 2Swansea University, UK — 3IMO - Hasselt University, Belgium

Photodetectors (PDs) find broad applications in many fields of optics. While inorganic PDs are widely used, they lack in easy processability and narrow-band detection. Organic PDs can fulfill these demands, providing many further advantages in comparison to inorganic PDs. The limiting factor of OPDs is their low detectivity, mostly caused by high dark current (JD) at reverse bias. Traps and sub-gap states are often observed in organic materials. Here, we investigate their effect on JD. We observe that JD follows a trend with the energies of the sub-gap CT states (ECT). Furthermore, in specific donor:C60 blends, we find trap concentrations of around 1016 cm−3 with an energy of around 0.5 eV below the transport level of C60. We intentionally vary the trap concentration in these blends and observe that*JD scales accordingly. Dark current-voltage simulations show that the expected value of*JD increases four orders of magnitude and rules the dark JV characteristics, when traps are included. The dependence of JD on reverse bias can be understood as an enhanced detrapping by means of Poole-Frenkel effect. These results point out to a physical process that might be general in donor:acceptor structures, explaining the high*JD commonly observed in OPDs. Moreover, optimized devices show JD as low as 500 pA cm−2 at -1 V, and on/off ratio of 107.

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